Summary Cryptosporidium remains a significant AIDS-related opportunistic infection among people with late HIV diagnosis or without access to HAART. This parasite infects the gastrointestinal (GI) epithelium in humans; infection is also a common cause of diarrhea in young children in developing countries. There is currently no fully effective therapy available for the infection. This parasite has been referred as a ?minimally invasive? mucosal pathogen, and epithelial antimicrobial defense is key to mucosal innate anti-Cryptosporidium immunity. Whereas it is well appreciated that IFN-? is required for preventing development of intestinal cryptosporidiosis, the key cellular regulatory elements that determine IFN-?-mediated GI epithelial anti- Cryptosporidium defense, as well as its association with the high susceptibility of infection in AIDS patients and in young children, remain unknown. Our recent studies demonstrate that IFN-?-mediated epithelial anti- Cryptosporidium defense requires the induction of specific long intergenic non-coding RNAs (lincRNAs) in epithelial cells. Specifically, we have identified several lincRNAs that are expressed strictly in epithelial cells. Expression levels of several epithelial lincRNAs are upregulated in GI epithelial cells following Cryptosporidium infection. Knockdown of selected epithelial lincRNAs attenuated IFN-?-mediated epithelial anti-Cryptosporidium defense. Based on these observations, we hypothesize that induction of epithelial lincRNAs in GI epithelial cells upon pattern-recognition receptors signaling promotes mucosal anti-Cryptosporidium immunity through priming epithelial cells for IFN-?-mediated epithelial antimicrobial defense. We will use in vitro and in vivo infection models and complementary biochemical, molecular, and morphologic approaches to define the transcription of epithelial lincRNA genes upon pattern-recognition receptor signaling in GI epithelial cells following Cryptosporidium infection (Aim 1), elucidate the molecular mechanisms by which epithelial lincRNAs promote IFN-?-mediated epithelial anti-cryptosporidial defense (Aim 2), and decipher the roles of specific RNA- binding proteins in modulating IFN-?-mediated anti-cryptosporidial defense in GI epithelial cells through their interactions with epithelial lincRNAs (Aim 3). The proposal is conceptually innovative as it tests new concepts regarding mucosal antimicrobial defense and the pathogenesis of intestinal cryptosporidiosis, relevant to the design and implementation of new therapeutic strategies.